3-difluoroaminomethyl-3-difluoroamino-oxetane and polymers thereof



United States Patent Ofitice 3,347,801 Patented Oct. 17, 1967 3,347,8013-DIFLUOROAMlNOMETHYL-3-DIFLUOROAMINO- OXETANE AND POLYMERS THEREOFEugene L. Stogryn, Fords, N.J., assignor to Esso Researchand'Engineering Company, a corporation of Delaware No Drawing. FiledNov. 16, 1962, Ser. No. 239,102 9 Claims. (Cl. 260-2) This inventionrelates to a novel high-energy polymerizable heterocyclic compound,polymers thereof, and the synthesis of the compound and the synthesis ofthe polymers.

The new high-energy polymerizable monomer is the N F adduct of3-methylene oxetane, termed'B-difluoraminomethyl 3-difluorarninooxetane, synthesized in accordance with the following general equation:

8-Methy1eue oxetane B-difluoramino oxetane Difiuoramino-containingcyclic. ethers, known as epoxides, have been prepared for polymerizationto higheuergy binders to be used in solid rocket propellants. Suchepoxides contain a 3-membered epoxy or oxirane group, shown as follows:Polymerization of the NF -containing epoxides is relatively slow andgenerally the polymerization yields oily or relatively low molecularweight polymers, which contain primary as well as secondary hydroxylgroups. The diiference in reactivity of the terminal OH groups,depending on whether they are primary or secondary, tends to make therate of reaction of these groups nonuniform in curing the polymers, asby reaction with cross-linking agents or chain-extending reactants.

In accordance with the present invention, it has been 'found thatpolymers formed from 3-difluoraminomethyl 3-difluoramino oxetane haveimproved physical and chemical characteristics in their utilization forpreparing high-energy binders as compared to NF -containing polyethersformed from epoxides. The polymers of the oxetane are represented by thefollowing recurring unit formula:

The recurring monomeric unit shown will have terminal hydroxyl, OH,groups attached to the methylene structure, has an NF group on atertiary carbon atom in the polymer chain nucleus.

Another distinguishing characteristic of the oxetane polymer compared topolyethers formed can be attributed to the chain structure shown in themonomeric unit. The monomeric unit of the polymer from the oxetane hasone more carbon atom in the chain per unit than the monomeric unit ofpolymers formed from the epoxides. This difference is believed tocontribute to greater strength and elasticity of the oxetane polymers onthe basis that the side chain or pendant groups do not contribute to thestrength of the polymer, but rather the numbers of atoms incorporatedinto the backbone or chain of the polymer. Where the end use of the NFcontaining polymers is a chain-extending or cross-linking type ofreaction, such as with diisocyanates, the strength of the polymersformed from the oxetane should have a distinct advantage.

Although modifications may be made in the synthesis of the N F adduct ofthe oxetane monomer and of its polymerization, the following examplesgive a detailed description of processes used for the preparation of thedesired compounds. The monomeric compound 3-methylene oxetane used forthe purpose of the present invention has been prepared according to theprocedure described by D. E. Applequist and J. D. Roberts in the Journalof American Chemical Society, vol. 78, page 4022 (1956). Alternativeprocedures have been used also for preparing this compound.

Example L-Preparation of the N F, adduct of 3-methylene oxetane3-methylene oxetane, 7.14 mmoles, is dissolved in 2 mls. of Freon 113 (CCl F This solution is placed in a Fischer-Porter glass pressure reactorof approximately 13 ml. capacity. After degassing, l4 mmoles of N F areintroduced into the reactor and the temperature is raised to C. and heldthere for 5 hours. After removal of excess N F the reactor is placed ina bath held at 20 C. and allowed to equilibrate with a previouslyevacuated trap which is maintained at a temperature of 76 C. By thisprocedure the Freon 113 is removed. A gas chromatographic analysis ofthe crude product indicates that essentially all of the Freon 113 hasbeen re-' moved. The weight of the crude product equals 1.14 grams. Thecrude product can be redistilled by a trap-totrap distillation using awarm-water bath. The infrared and the proton and fluorine NMR spectraare in excellent agreement with the structure 3-difluoraminornethyl 3-difluoramino oxetane. Calculated for C H ON F Percent C, 27.6; percentN, 16.1; percent F, 43.6. Found: Percent C, 27.4; percent N, 16.1;percent F,'43.8.

Addition of N F to 3-methylene oxetane proceeded smoothly and withoutcomplications under the conditions described, particularly in using theexcess N F and using 5 mmole percent NaF in the mixture of thereactants. 'Ilhe sodium fluoride, NaF, acted as a butter to eliminatethe formation of polymers during difiuoramination.

In general, the addition reaction of N F withthe 3- methylene oxetane isindicated to take place at a reaction temperature in the range of about25 to C. in the presence of a halohydrocarbon solvent or inert diluent.

The resulting adduct having the 4-membered heterocyclic ring with the NFgroup linked to car-hon in the 3 position of the ring and an NF grouplinked to themethylene group which is directly linked to the 3 positioncarbon has a structure such as has been identified and which is termed3-difluorarninomethyl 3 difiuoramino oxetane. This compound proved to bereadily polym erizable under very mild conditions with cationiccatalysts, such as PF and BF The resulting polymers were from epoxidesgenerally colorless or a very pale yellow, with molecular weightsranging from about 1,000 to 10,000. The polymers were tacky materialswhich could be drawn into strands. Low molecular weight polymers, whichwere viscous oils, were obtained at low polymerization temperatures withshort polymerization reaction periods and with the use of modifiers suchas H and alcohol, e.g. 1,1,l-trimethylol propane. The higher molecularweight polymers, 5,000+molecular weight, were semi-solid to solid andthese were elastic. The infrared and elemental analyses of the polymersshowed that the NF groups remained intact and attached to the carbonatoms during the polymerization using the procedure set forth in thefollowing examples.

Example 2.P0lymerizati0n 0f 3-difluo raminomethyl 3-diflu0ramin0 oxetane3 difluoraminomethyl 3 -difluoramino oxetane, 0.4 g. was introduced intoa suitable polymerization vessel. The reactor was cooled to 196 C. withthe use of a liquid nitrogen bath and 6.5 mole percent PF was condensedin the reactor. The reactor was then allowed to warm up to the desiredtemperature of polymerization and held there for a predetermined periodof time.

The polymerization was terminated by removal of catalyst, either bypumping it off or shaking with a dilute Na CO solution, or both. Thepolymers recovered had the recurring unit composition [C H ON F thesubscript n signifying, in conventional manner, the number of units permolecule, e.g. in the range of about 4 to 80 and more, depending on themolecular weight.

Polymer products obtained were found to contain as many as 1.7 to 2 OHgroups per molecule. Such high values of hydroxyl/polymer molecule aredesirable in chain-extension and cross-linking compounds havingfunctional groups that react with the OH groups or the reactive H ofthese groups.

Variations can be made in the procedure as to catalyst, catalystconcentration, time, temperature, the use of solvents, e.g.halohydrocarbon, and modifiers for varying the molecular weight of thepolymer product and also for variations in the terminal groups, ifdesired.

The following table summarizes a number of typical variations inpolymerization conditions, catalyst, and use of modifiers and solvents,with results achieved.

TABLE I.--POLYMERIZATION OF 3'DIFLUORAMINO- METHYL 3-DIFLUORAMINOOXETANE 0 Figures show mol percent catalyst based on monomer.

b Indicates rnol percent modifier based on monomer.

0 Figures indicate molecular weight of polymer obtained from solution ofthe polymer in acetonitrile.

d TMP is 1,1,1-trimethyiol propane as hydroxyl group-containingmodifier.

e Viscous oil.

The elemental analysis of the polymers demonstrates the preservation ofthe N1 groups during the course of polymerization. Calculated for [C HON F percent C, 27.6; percent N, 16.1; percent F, 43.6. Found: percentC, 26.42; percent N, 15.5; percent F, 43.8.

It was thus demonstrated that the bis(NF adduct of the methylene oxetanemonomer can be polymerized readily with a variety of catalysts of thetype useful in forming polyethers which, in general, includes metal andmetalloid halides. The higher molecular weight polymers formed from thebis(difluoramino) adduct of methylene oxetane monomer are sufficientlystrong and elastic to be used as a binder in forming a propellantcomposite having a high impulse value, as indicated in the followingformulation:

Component: Wt. percent Liquid tetrakis NF (butane) 35 NH ClO (oxygenoxidizer) 40 Boron powder (fuel) 5 [C4lIsONgF41 Isp 300 The above is atypical formulation which can be varied by using other fuels, such aspowdered metals of the group consisting of boron, beryllium, aluminum,magnesium, lithium and hydrides of such metals; other fluorine (NF andoxygen oxidizers, such as tetrakis (N1 tetrahydrofuran, hydrazineperchlorate, hydrazine nitroform, ammonium perchlorate, and variousothers known or to be developed. The binder is represented by therecurring polymeric unit in the bracket as being the polymer of 3difluoraminomethyl 3 difiuoramino oxetane. The polymers of the N Fadduct of methylene oxetane can be reacted to undergo chain-extension orchain crosslinking with reactants, such as diisocyanates which formpolyurethanes, or with reactants such as acrylic acid which formpolyester linkages, in order to give the polymers a further increasedmolecular weight, strength, and elasticity. The reaction of the polymersis illustrated by the following example.

Example 3 .--Chain-extensi0n polymerization Poly 3 difluoraminomethyl 3difluoramino oxetane was dissolved in methylene chloride. To thissolution was added a catalytic amount of ferric acetylacetonate andtoluene diisocyanate in concentration required to bring aboutchain-extension polymerization of the polyether to a higher molecularweight polyurethane. The solution was placed on a steam-bath and allowedto cure to a light tan, tough, elastomeric polymer.

The energy values of the chain-extended and crosslinked polymers of3-difiuorarninomethyl 3 difiuoramino oxetane are high on account oftheir high NF content, i.e. close to 60%.

Modifications in conditions of reaction, proportions of reactants,solvents, and modifying conditions may be made within the spirit andscope of the invention claimed.

The invention described is claimed as follows:

1. 3 difiuorarninomethyl 3 difiuoramino oxetane having the composition CH ON F and the structural formula:

2. Polymers of 3 difiuoraminomethyl 3 difluoramino oxetane having therecurring unit:

i r t a r-r H NF: B

3. Polyether polymers of 3-difluoroaminomethyl 3-difluoroamino oxetanehaving a molecular weight in the range of about 1,000 to about 10,000.

4. Method of preparing the N F adduct of 3-methylene oxetane whichcomprises reacting 3-rnethylene oxetane with N 1 to form an additionproduct having a composition of C H ON F and recovering said additionproduct.

5. Method of preparing 3 difiuoraminomethyl 3-difluoramino oxetane whichcomprises reacting 3-methylene oxetane with excess N F for additionreaction of one mole of N F with one mole of the 3-methylene oxetane ata reaction temperature in the range of 25 to C. in the presence of aninert diluent, and recovering as rerange of about -30 C. to about 60 C.,and recovering 1 a resulting polyether polymer.

8. The method of claim 7, in which the polymerizing is carried out inthe presence of an inert diluent.

9. The method of claim 7, in which the polymerizing is carried out inthe presence of a hydroxyl group-con- 5 taining modifier.

References Cited Farber: Astronautics, 1960, pp. 34, 40 and 42.

Hoffman et al.: Chemical Reviews, vol. 62 (February I SAMUEL H. BLECH,Primary Examiner.

1. 3-DIFLUORAMINOETHYL 3 -DIFFLUORAMINO OXETANE HAVING THE COMPOSITIONC4H6ON2F4 AND THE STRUCTURAL FORMULA:
 2. POLYMERS OF3-DIFLUORAMINOMETHYL 3- DIFLUORAMINO OXETANE HAVING THE RECURRING UNIT: